APPLICATION OF X-RAY TOMOGRAPHY TO THE CHARACTERIZATION OF SINGLE GRANULES
Advancing the chemical engineering fundamentals
Particulate Systems (T2-3)
Keywords: granulation, x-ray tomography, granule strucutre
D. Barrera-Medrano1,2, G.K. Reynolds2, A.D. Salman2, M.J. Hounslow2
1 BASF Aktiengesellschaft, GCT/T – L540, 67056 Ludwigshafen, Germany
2 Particle Products Group, Department of Chemical and Process Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK
Fine particulate systems play a very important role both in day-to-day life and in human economy. Over 70% of industrial manufacturing processes (including pharmaceutical, chemical and food industries) involve small solid particles ranging from low-cost materials such as agricultural grains or sand, to the more specialized and expensive such as pharmaceutical products.
When dealing with particulate solids it is common in industry to aggregate them together in order to form larger entities by a granulation step, in order to improve the properties of the product (such as increased flowability or reducing of dustiness). This work focuses on wet granulation, which can be defined as the process of agglomerating fine powders in the presence of a liquid binder in order to obtain a smaller number of larger particles (granules).
The structure of granules is a key factor in determining the final properties of the product, whether as independent agglomerates or tablets. It would be therefore very important to understand how the structural characteristics of an agglomerate are going to affect its properties, as well as how the way the agglomerates have been manufactured is going to affect the structure of the agglomerate. However, research has traditionally focused on trying to relate formulation/process parameters to the properties exhibited by the products, but usually the effect of these parameters on the structure is overlooked. In this research X-ray tomography (XRT) was used in order to study the structure of single agglomerates and how it is affected by the different parameters used in the granulation process.
XRT is a technique that uses x-rays to evaluate non-destructively the internal microstructure of objects. It has widely been used in medical imagery since it was first discovered in the 1960s and 1970s. However its potential in the powder technology area has only started to be realized recently. A commercial desktop XRT system was used to scan single granules and a method developed to analyze the raw data generated in terms of radial profiles of greyscale intensity within the granules in order to provide information of the internal structure of the granules.
Different granulation methods and materials were studied and a deeper research carried out in the case of high-shear melt granulation investigating the effect of process and formulation parameters in the structure exhibited by the resulting granules.
As an example, the presence of a core of unmixed binder in granules manufactured via melt-in agglomeration was observed at early granulation times, and depending on factors such as the impeller speed used these binder cores could still be seen even after granulation times up to 15. The presence of a core of binder illustrates that immersion is the prevalent nucleation mechanism in the experiments performed.
Presented Monday 17, 15:40 to 16:00, in session Particulate Systems (T2-3).
